A convolution model to calculate the
photon flux of other model components. For example :

cpflux*phabs*(pow + gauss)

with the normalization of the
power-law model fixed to a non-zero value gives the photon flux and error on
the entire model.

phabs*cpflux*(pow + gauss)

again with the normalization of the
power-law fixed to a non-zero value gives the unabsorbed photon flux and error.
Finally,

phabs*(pow
+ cpflux*gauss)

with the normalizaton of the
gaussian fixed to a non-zero value gives the photon flux and error on the
gaussian component. Note that when the cpflux model is used the normalization
of one of the additive models must be fixed to a non-zero value. It is
also important to ensure that the energy range over which the model is
calculated (which is determined by the response matrix in use) covers the
energy range for which the photon flux is calculated. If the model to which the
cpflux is applied integrates to zero then a divide-by-zero error will occur
resulting in NaN values for the fit statistic.